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bioRxiv · 10.1101/2025.03.20.644365

Influence of Copper Dose on Mycobacterium avium and Legionella pneumophila Growth in Premise Plumbing

Smeltz, R. E.·Roman, F. A.·Bryne, T.·Finkelstein, R.·Song, Y.·Pruden, A.·Edwards, M. A.
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Abstract

Effects of copper at 0, 4, 30, 250, or 2000 {micro}g/L on microbial communities were examined in an 11-month study using triplicate 120-mL water heater microcosms with PEX-b pipes containing mature biofilms to simulate premise plumbing. Effluent total cell counts (TCCs) and Mycobacterium avium peaked at 250 {micro}g/L, reflecting the dual role of copper as a nutrient and antimicrobial. TCCs and M. avium were relatively consistent among replicate microcosms at each dose, but Legionella pneumophila (Lp) diverged among biological triplicates at 250 {micro}g/L, consistently producing high culturable Lp (average 2.5 log MPN/mL) in one microcosm and low/non-detectable levels in the other two. Repeated cross-inoculations and a reinoculation failed to normalize the microbial community composition across 250 {micro}g/L and other triplicate microcosms. 16S rRNA gene amplicon sequencing revealed that the 250 {micro}g/L replicate with high Lp was characterized by a distinct microbial community composition relative to the two replicates. At 2,000 {micro}g/L copper, microbial diversity and TCCs initially decreased, but then TCCs subsequently increased and ultimately were not statistically different from the 250 {micro}g/L microcosms. This study provides insight into mechanisms underlying non-linear effects of copper dosing when applied as a disinfectant to premise plumbing for opportunistic pathogen control. SYNOPSISNon-linear effects of copper on Legionella pneumophila and microbial communities are identified, providing deeper understanding to the efficacy of its use as a premise plumbing disinfectant.

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Smeltz, R. E., Roman, F. A., Bryne, T., Finkelstein, R., Song, Y., Pruden, A., Edwards, M. A.. 2025-03-20. Influence of Copper Dose on Mycobacterium avium and Legionella pneumophila Growth in Premise Plumbing. https://doi.org/10.1101/2025.03.20.644365

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